Power semiconductor devices and other transistor and integrated circuit devices that dissipate high power, or are used in high frequency telecommunications, generally are packaged with a heat sink (or heat slug) to dissipate heat produced by the device, and to provide RF ground for the device. The heat slug is positioned close to or against the semiconductor device and encapsulated within the device package with one surface of the heat slug exposed through the package encapsulant. The addition of the heat slug along with the lead frame requires additional assembly steps, additional equipment, and adds cost to the package. Also, voids between the heat slug and device can cause package problems and device malfunctions. Large low profile packages require "dry packing" to insure that "popcorn cracks" do not occur during device-to-PWB (Printed Wiring Board) soldering. "Popcorn cracks" are generally caused by rapid heating and resulting expansion of moisture between the large die pad and the thin bottom plastic of the device package.
The use of heat slugs in a package consumes a large portion of the total internal height of the package which prevents this approach from being used in low profile packages. Low profile packages are often required in equipment such as disk drives, notebook computers, cellular phones, PCMCIA cards, personal digital assistants and portable consumer electronics.